Organoborosiloxazane polymers

Abstract

Preceramic polymers which have particular utility in providing protective ceramic coatings on carbon/carbon composites, graphite, carbon fibers, and other normally oxidizable materials are prepared by reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysiloxazane in an organic solvent to form an organoborosiloxazane polymer.

What is claimed is: 
     
       1. A process which comprises reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysiloxazane in an organic solvent to form an organoborosiloxazane polymer. 
     
     
       2. The process of claim 1 wherein the boroxine is a compound corresponding to the formula: ##STR2## in which R' is an alkoxy, phenoxy, alkylphenoxy, phenalkoxy, or alkylphenalkoxy substituent in which any alkyl or alkoxy group contains 1-6 carbons. 
     
     
       3. The process of claim 2 wherein the boroxine is trimethoxyboroxine. 
     
     
       4. The process of claim 1 wherein the polysiloxazane is a polymer prepared by reacting a poly(silylamide) with a polysiloxane having a plurality of repeat units of the formula [RSi(H)O] n  wherein R is an alkyl group containing 1-6 carbons, a cycloalkyl group containing 3-6 carbons, or a substituted or unsubstituted aryl group containing 6-10 carbons, and n is an integer of at least one. 
     
     
       5. The process of claim 1 wherein the boroxine is a trialkoxyboroxine and the boroxine/polysiloxazane weight ratio is about 1-6/1. 
     
     
       6. The process of claim 5 wherein the boroxine/-polysiloxazane weight ratio is about 3-4/1. 
     
     
       7. The process of claim 1 wherein about 3-4 parts by weight of trimethoxyboroxine are mixed with a solution of one part by weight of a polysiloxazane in an organic solvent; the polysiloxazane being a polymer prepared by reacting a poly(silylamide) with a polysiloxane having a plurality of repeat units of the formula [RSi(H)O] n  wherein R is an alkyl group containing 1-6 carbons, a cycloalkyl group containing 3-6 carbons, or a substituted or unsubstituted aryl group containing 6-10 carbons, and n is an integer of at least one. 
     
     
       8. An organoborosiloxazane polymer prepared by the process of claim 1. 
     
     
       9. An organoborosiloxazane polymer prepared by the process of claim 2. 
     
     
       10. An organoborosiloxazane polymer prepared by the process of claim 3. 
     
     
       11. An organoborosiloxazane polymer prepared by the process of claim 4. 
     
     
       12. An organoborosiloxazane polymer prepared by the process of claim 5. 
     
     
       13. An organoborosiloxazane polymer prepared by the process of claim 6. 
     
     
       14. An organoborosiloxazane polymer prepared by the process of claim 7. 
     
     
       15. A composition which comprises a solution of 5-75% by weight of an organoborosiloxazane polymer in 95-25% by weight of an organic solvent; the polymer being the product obtained by reacting about 0.25-20 parts by weight of a trialkoxy-, triaryloxy-, or tri(arylalkoxy)boroxine with one part by weight of a polysiloxazane in an organic solvent. 
     
     
       16. An article which comprises a substrate and a coating derived from the composition of claim 15. 
     
     
       17. A ceramic derived from the organoborosiloxazane of claim 8.